JP3145697B2 - Flue gas purification method - Google Patents

Abstract

A method for purifying flue-gases and other hot, oxidative waste gases originating from industrial installations, combustion furnaces, engines and the like, whereby the hot gas to be purified is passed through at least one spraying chamber or -area and is contacted therein with a gas washing liquid, which is sprayed into the hot gas flow and cools the gas to below 100 DEG C, whereby residual liquids with a high chemical oxygen consumption value, which comprise complex builders, compounds of heavy metals, sulphur- and nitrogen compounds, and originating amongst others from fixing-baths and the like from the photographic, photochemical and galvanic industries, are used as gas washing liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying flue gas and other hot, oxidizing waste gases derived from industrial equipment, combustion furnaces, engines and the like.

Flue gases from fireplaces, engines, factories, etc. generally contain solid matter (fly gas), gaseous compounds and steam. This flue gas contains many heavy metal compounds, acid gases,
For example, HBr, HCl, HF, SO 2, NO X, and a gas, for example,
N ₂ , O ₂ , CO and CO ₂ are often found.

Flue gas loaded in this way can include, among other things, “acid rain” (eg, due to sulfur dioxide and ammonia),
Direct emissions to the environment in connection with “greenhouse effects” (CO ₂ ), soil pollution (eg, by dioxane), and groundwater pollution are burdensome to the environment. Fly ash is also extremely harmful in connection with mist formation (smog), which causes the entire atmosphere to be loaded with substances that are harmful to health and often even very toxic. For this reason, it is desirable and often enforced that this flue gas be purified before it is released to the atmosphere.

In practice, dust is removed by cyclones, filters, textile filters and electrostatic filters. Filtration is performed after the temperature is reduced to about 300 ° C or less.
Slow cooling of the gas from ± 1200 ° C to 300 ° C causes the formation of dioxane and benzofuran.

Gaseous components are washed out by washing with a liquid containing lime. Also in fireplaces in this way, for example, lime is often injected in order to bind the SO _2. Sometimes an alkali is used as a reactant. This gas cleaning liquid is drained directly or after processing. Possible slurry is discarded.

Such a method of purifying flue gas has the drawback that complete purification cannot be obtained, and that many harmful substances, metal compounds, gases and the like are released to the atmosphere and the environment.
In addition, there is a significant problem of dioxane, which is released during the gradual cooling of the flue gas, especially for the combustion of waste.
Furthermore, the gas cleaning solution itself places a new burden on the environment.

It is an object of the present invention to provide a method for purifying flue gas containing dust and acid gases, whereby almost complete purification has been achieved and environmental concerns have been reduced to a minimum.

For this purpose, the present invention provides that the hot gas to be purified is passed through at least one spray chamber or section and is internally contacted with a gas cleaning liquid which is sprayed into the hot gas stream and cools the gas to below 100 ° C. In this case, a residual liquid having a high CZV value (scientific enzyme consumption value) is used as a gas cleaning liquid, which contains complex builders, compounds of heavy metals, compounds of sulfur and nitrogen, and a few from the photographic, photochemical and plating industries. A method was provided for purifying flue gas as described in the introduction, characterized in that it originated from a fixing bath or the like.

The following are possible residual solutions: a) the residual solution obtained in part by a metal removal photographic bath (fixing-developer-stop bath), b) the residual solution obtained after ONO-treatment of the plating bath, c) the composite Residual liquid containing builders such as borofluoric acid, EDTA (ethylene dinitrotetraacetate), silicofluoride and the like.

No. 8,902,489, of the same applicant and of the same rank, discloses that the residual liquid to be treated is sprayed into a hot oxidizing gas stream originating from industrial installations, combustion furnaces, etc. A method of treating this residual liquid by treating the condensate recovered for removal of sulfur compounds and the like is suggested.

It has now been found, conversely, that this treatment using this residual liquid as a gas cleaning liquid can remove heavy metals, sulfur compounds and other impurities from this hot oxidizing gas. Due to strong mixing with the residual liquid used as the cleaning liquid, the power of this gas stream is used for the formation of steam, fry gas, part of the supplied gas is taken into the cleaning liquid, and many reactions This leads to the formation of insoluble components, which settle in the spray chamber or in the lower part of the gas scrubbing reactor. This causes an oxidation-reduction step as described in the aforementioned Dutch patent application. This results in a purification of the flue gas, whereby the material to be removed partially precipitates, partially dissolves in the washing liquor and is partially converted to a less harmful gas. The saturated vapor remaining in the spray chamber or gas scrubbing reactor contains liquid droplets, which are separated therefrom.

A major advantage with the present invention is that the hot flue gas is rapidly cooled from high temperature to ± 60-70 ° C. by spraying a gas flushing liquid, thereby preventing the formation of, for example, dioxane and benzofuran.

Another advantage is that the gas scrubbing liquid or residual liquid used is chemically converted in such a way by strong contact with the oxidizing flue gas, so that environmentally harmful impurities such as those described in the aforementioned Dutch patent application. It can be removed by the method. Thus, a dual purpose is obtained: on the one hand, highly contaminated flue gases are purified and, on the other hand, for example, the simultaneous conversion into a form in which the residual liquid of the fixing bath can be further decomposed into substances which are not harmful to the environment. it can.

In the process according to the invention, the spraying of the gas cleaning liquid is preferably carried out in such a way that the gas to be purified is cooled to 60-70 ° C.

Advantageously, the gas saturated with the cleaning liquid is sent from the spray chamber to the liquid / vapor separator and the separated cleaning liquid is recycled and sprayed again into the hot gas stream.

This effectively sends the recycle stream of gas scrubbing liquid to the purification stage, where the various components are decomposed and removed.

As already described in Patent Application No. 8902489, the recycle stream of gas scrubbing liquid is thereby subjected to electrolysis and iron cementation, where heavy metals precipitate, and the pH of the recycle stream is preferably hydroxylated. The addition of calcium raises it to 5 or more due to the precipitation of heavy metal hydroxides.

For silver precipitation, a halide is further added to the gas scrubbing liquid. Generally, the flue gas itself contains the appropriate halide.

By adding calcium and nitrate ions to the gas cleaning fluid sprayed into the flue gas, harmful gases,
For example, an effective means is provided for removing sulfur dioxide and ammonia. Heavy metals such as Cu ⁺⁺ , Fe ⁺⁺⁺ , A
In the presence of ions such as g ^+, SO ₂ dissolved in the washing solution is SO ₄
^- can be converted to ions, which subsequently precipitate with calcium by the reaction mechanism ^{below: (. Kat.Cu ++ Fe +++ Ag} + enz) SO 2 + oxidizer _{+ → SO 3 SO 3 + H} 2 O → 2H ⁺ + SO ₄ ¹¹ SO ₄ ¹¹ + Ca ⁺⁺ → CaSO ₄ ↓ Lead sulfate reacts separately from calcium sulfate SO ₄ + Pb ⁺⁺ → PbS
Precipitate similarly with O ₄ . Thus, the lead ions from the hot flue gas can be removed in an effective manner. The ammonia in the retentate, which is converted to ammonium ions, reacts with the nitrate ions in the retentate according to the following equation: Oxygen generated thereby further contributes to decomposition by oxidation of the composite compound in the residual liquid.

The residual liquid used as a gas cleaning liquid usually contains
There is EDTA- complexes, which are gradually oxidized by oxidizing substances from the gas stream, and ^{Fe +++, Cu ++, Hg +} , Ni ++ and
Ag ⁺ ions are further important for catalytic oxidation.

It is desirable that there be an excess of free Fe ⁺⁺⁺ ions, especially in relation to the EDTA complex. This forms the most stable EDTA complex, and this allows the appropriate metal to be replaced with another metal-EDTA
Can be released from the complex. Degradation of EDTA takes place by the reaction mechanism below: Metal complex with _{EDTA = MeH 2 · EDTA MeH 2} · EDTAMe ++ = H 2 · EDTA H 2 · EDTA + oxidizer + catalyst _{→ N 2 ↑ + xCO 2 ↑} + yH 2 O The process according to the invention is preferably performed in a number of gas scrubbing steps. The hot flue gas to be purified thereby is pre-purified in a first washing stage and cooled to below 100 ° C. and subsequently passed through a cascade of stacked washing stages,
This allows each scrubbing step to have its own scrubbing liquid recirculation so that the temperature of the flue gas is gradually reduced to 50-60 ° C. After all, the gas passing through all stages can be released to the atmosphere without any obstacles.

The invention will be further elucidated by a gas scrubbing reactor system suitable for the method according to the invention in connection with the drawings.

FIG. 1 shows a schematic side view of a reactor system for purifying flue gas by gas scrubbing according to the method of the present invention. The system has a central washing column 2 to which a washing reactor 1 forming the first washing stage of the system is connected by a liquid-vapor separator 3. Below this liquid-vapor separator 3 is a cleaning liquid drain 4, which is connected to a gas cleaning liquid recirculation and purification system.

This central washing column 2 consists of a number of superimposed washing steps, shown as washing steps 5, 6 and 7 in the example. Each of these cleaning stages has a sprayer at the bottom for gas cleaning liquid, a Venturi jet tube 8 is shown in the example. Each washing stage is separated by a droplet collector 9 at its upper end from the next.

Below the lower washing stage 5 of the central washing column 2, which constitutes the second washing stage of the whole system, there is a tank for washing solution, and the remaining stages 6 and 7 each have a separate washing solution tank 11. Each of these wash tanks is coupled to a recirculation system, where a pump 12 undertakes recirculation.

In this lower washing step, the draining liquid is
In a washing stage placed directly above the venturi tray 13, the draining liquid is returned to the associated tank 11 by a lateral drain.

The apparatus operates as follows: The flue gas is passed to a first cleaning reactor 1, not shown in detail, and as described above, for example, a gas cleaning liquid consisting of residual fixing liquid in the fixing bath and in the reactor. Contacted by The pre-purification of the flue gas takes place as a result of the redox process taking place between the gas cleaning liquid and the flue gas, while the liquid 4 draining from the liquid vapor separator is recycled and purified. In this way, pre-purification of the flue gas and purification and decomposition of the residual fixing solution used as a washing solution in this example can be simultaneously obtained.

The pre-purified flue gas containing steam enters following the lower (second) washing stage 5 of the central washing column 2, where it is contacted by a venturi jet tube 8 with washing liquid which is sprayed upward. This allows further purification to take place by chemical reaction, and the drop collector 9 of the lower stage 5 allows excess liquid to drip back into the tank 10. This flue gas is carried together by a jet directed upward from the venturi jet tube 8 and rises, and enters the next washing stage 6, where a similar gas treatment is carried out with the venturi jet tube 8 and the tank 11 Caused by the circulation system of the pump 12.

This washing stage 6 and the subsequent washing stage 7 are further provided with a venturi tray 13, which causes the liquid coming from the droplet collector 9 to enter the circulation system for the washing fluid in this stage and thus has a constant Ensure circulation.

This gas is again carried upwards to the next stage, where a similar process takes place. At the upper end of the last washing stage 7, a water shower is arranged above the drop collector 9, which causes further cooling of the already cooled gas in the meantime.

The liquids of the second, third and fourth stages, 5, 6 and 7, respectively, in the whole system are treated separately and act after treatment as an aid to the evaporant of the first washing reactor 1. In a practical embodiment, the gas passage input of the first cleaning reactor is between 6,000 and 10,000 Nm ³ /
The amount of time can be reached.

It is possible to connect one or more first washing reactors 1 to a central washing column. FIG. 2 shows a schematic top view of a system in which four first washing reactors 1 are connected to a central washing column 2, each of which is separated therefrom by a liquid vapor separator 3. The advantage of this system is that, for example, in the case of flue gas from the furnace, the furnace process can be continued even if a defect that requires shutting down occurs in one of the gas cleaning reactors 1. If one of the washing steps of the central column is stopped, the other steps can continue to work in the usual way.

The present invention has been disclosed above with a particular type of wash reactor system. It will be apparent that the invention is not tied to this particular system, and that other systems are possible for applying the invention.

[Brief description of the drawings]

FIG. 1 shows schematically an apparatus for application of the method according to the invention, having a first washing stage connected to a central washing column on which a number of washing stages are superimposed. FIG. 2 schematically shows a top view of a central washing column with a number of first washing stages connected.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/50 B01D 53/34 125P 53/58 131 53/64 136Z 53/77 (56) References JP-A-52-68888 ( JP, A) JP-A-51-119379 (JP, A) JP-A-52-128882 (JP, A) JP-A-53-89882 (JP, A) JP-A-55-88827 (JP, A) Hei3-188986 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/14 B01D 53/18 B01D 53/40 B01D 53/50 B01D 53/58 B01D 53/64 B01D 53/77

Claims (10)

(57) [Claims] Claims 1. An industrial facility, an incinerator or an engine.
A method for purifying oxidative waste gas or flue gas above 100 ° C., comprising the following steps: (a) passing said gas through at least one spray chamber or spray area; Simultaneously spraying a gas cleaning solution containing a composite builder, a heavy metal compound, a sulfur-containing compound and a nitrogen-containing compound and containing a residual solution derived from a photographic fixing bath, a photochemical fixing bath or a plating fixing bath for contacting with the gas. (C) cooling the gas to below 100 ° C .; (d) purifying the gas cleaning liquid by subjecting the gas cleaning liquid to toxic compound removal means; and (E) removing harmful impurities from the gas selected from the group consisting of acid gases, heavy metal compounds, sulfur compounds, and dust. The method further comprising simultaneously purifying the gas cleaning liquid as a result of contacting the gas cleaning liquid with the gas. 2. The gas to be purified is 60
The method according to claim 1, wherein the method is cooled to −70 ° C. 3. The method according to claim 1, wherein the gas from the spray chamber saturated with the cleaning liquid is passed to a liquid-vapor separator and the separated cleaning liquid is recycled and sprayed again into the gas stream. A method according to claim 1 or 2. 4. The process according to claim 3, wherein the gas cleaning liquid of the recycle stream is subjected to electrolysis and iron cementation. 5. The process according to claim 4, wherein the pH of the recycle stream is raised to 5 or more due to precipitation of the heavy metal hydroxide. 6. The process according to claim 5, wherein the pH of the recycle stream is raised by adding calcium hydroxide. 7. The method according to claim 1, wherein a halide is added to the gas cleaning liquid. 8. The flue gas is sprayed onto the flue gas with the addition of calcium and nitrate ions.
A method according to one of the preceding claims. 9. The method according to claim 1, wherein excess Fe ⁺⁺⁺ ions are provided in the gas cleaning liquid. 10. The flue gas to be purified is pre-purified in a first washing stage and cooled to below 100 ° C. and subsequently passed through a cascade of overlying washing stages, whereby each stage has its own Characterized in that it has a gas cleaning liquid circulation and the temperature of the flue gas gradually decreases to 50-60 ° C,
A method according to one of the preceding claims.